### University of Crete HEP Seminars

**
Super-Planckian scalars?
**

Speaker: | Lukas Witkowski |

Institution: | University of Crete |

Time: | Tuesday 26 September 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Scalar fields with super-Planckian field ranges play an important role in models of large-field inflation and are also employed in cosmological solutions to the electroweak hierarchy problem. One difficulty in constructing such models is that for super-Planckian field values quantum-gravitational effects cannot be ignored. In particular, ultraviolet physics is expected to constrain the field range over which scalars can exhibit a monotonic potential, which in turn has consequences for models of inflation. To study theories of super-Planckian scalars some knowledge of ultraviolet physics is thus necessary. String Theory is a candidate theory of Quantum Gravity and a suitable framework for addressing this question. Another approach is based on the Weak Gravity Conjecture – an as yet unproven theorem regarding consistent theories of Quantum Gravity. In this talk I want to report on recent progress in the study of super-Planckian scalars. In particular, I will explain how the existence of super-Planckian scalars is increasingly called into question by both String Theory and the Weak Gravity Conjecture. |

**
Holographic RG flows on curved manifolds
**

Speaker: | Lukas Witkowski |

Institution: | University of Crete |

Time: | Thursday 28 September 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | Holographic RG is based on the idea that the radial coordinate of a spacetime with asymptotically AdS geometry can be identified with the RG flow parameter of the boundary field theory. Holographic RG flows have been studied intensively for the case of field theories defined on a flat background manifold. In this talk I will consider the case where the background spacetime for the field theory is curved. In particular, I will consider the cases of field theories defined on a sphere as well as dS and AdS spacetimes. In this setting I will explore solutions that have exotic properties from a RG point of view. There is also tantalising evidence for the existence of first-order phase transitions triggered by a change in curvature. |

**
Title to be announced
**

Speaker: | Panagiotis Betzios |

Institution: | University of Crete |

Time: | Tuesday 3 October 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | TBA |

**
Elasticity and (pseudo)-phonons in holography
**

Speaker: | Matteo Baggioli |

Institution: | University of Crete |

Time: | Tuesday 10 October 2017, 14:15 |

Venue: | 2nd floor seminar room |

Abstract: | We discuss the presence and the physical features of (pseudo)-phonons in the context of the holographic framework. We present two different holographic models which show gapped (and damped) transverse and longitudinal phonons. In particular we emphasize the role of elasticity and we determine the speeds of propagation which turn out to be in good agreement with the theoretical expectations. Finally we comment on the optical conductivity and its DC limit with an eye on the physics of pinning and the recent proposals for bad metals. |